Thanks for your advice. I don't know if I can get hold of distilled water, but soft bottled water is affordable. I've done some B&W before in a photo club, but not on my own equipment. Now that I've moved away, it's rather a hassle to get to the club darkroom, so I figured it was more efficient to show up with developed negatives and spend my limited time there printing.

Is it ok to use tap water for washing and then bottled water for final rinse, or should I use bottled water for everything?

I had overlooked that XTOL is only available in 5 liter sets, which is inconvenient, so maybe I'll go for liquid developer after all.